Cone Beam CT Flashcards
What is CBCT?
a form of cross-sectional imaging suitable for assessing radio dense structures
What type of radiation is used for CBCT?
- ionising radiation
- x-ray
What shape is the beam used for CBCT?
pyrimidal/conical
What shape is the digital receptor used for CBCT?
square
How should the head be positioned for CBCT?
- horizontal
- Frankfort plane parallel with floor
- vertical
- midsagittal place
What are the benefits of CBCT over plain radiograph?
- no superimposition
- ability to view from any angle
- no magnification/distortion
- allows for volumetric reconstruction
What are the downsides of CBCT over plain film radiography?
- increased radiation dose
- lower spatial resolution
- susceptible to artefacts
- equipment more expensive
- images more complicated to manipulate
- images more complicated to interpret
- requires additional training
What are the main benefits of CBCT compared to conventional CT?
- lower radiation dose
- potential for sharper images
- cheaper
- smaller footprint
What are the main benefits of conventional CT compared to CBCT?
- able to differentiate soft tissue better
- cleaner images
- larger field of view possible
What are the most common uses for CBCT in dentistry?
- clarifying relationship between impacted mandibular third molar and inferior alveolar canal prior to intervention
- plain radiograph indicated close proximity
- measuring alveolar bone dimensions to help plan implant placement
- visualising complex root canal morphology to aid endodontic treatment
- investigating external root resorption next to impacted teeth
- if not clear on plain radiographs
- assessing large cystic jaw lesions and their involvement of important anatomical structures
What are the 3 common orthogonal planes used for CBCT?
- axial
- sagittal
- coronal
What is 3D volume reconstruction used for?
- picturing the extent/shape of a disease
- informative teaching aid for patient
What are the drawbacks of 3D volume reconstruction?
- modified reconstruction of data
- can be misleading
- particularly poor for thin bones
What imaging factors and variables are set before the scan and why?
- alter the information obtained
- alter the patient dose
- considered on case-by-case basis
- field of view
- voxel size
- acquisition time
What is the field of view in CBCT and what is the decision on size based on?
- the size of the captured volume of date
- decision based on clinical case
- increased size
- increased radiation dose
- increased tissues irradiated
- increased scatter
- larger report required
- increased size
What is the voxel size in CBCT and what is the decision on size based on?
- the image resolution
- voxels are 3D pixels
- CBCT larger than plain radiographs
- voxels are 3D pixels
- decision based on clinical case
- decreased voxel size increases dose
- decreased voxel size increases scan time
- typical range of voxel sizes
- 0.4mm3-0.085mm3
What imaging factor choices are used for endodontic cases?
- field of view as small as possible
- 5x5cm
- unless case with large apical pathology
- smaller voxel size
What imaging factor choices are used for implant planning cases?
- field of view depends on number and position of implants
- larger voxel size
What is the radiation dose delivered from CBCT?
- cannot determine single generic value
- equipment
- field of view
- position of field of view
- voxel size
- 13-82uSv
- studies show up to 674uSv
What are artefacts?
- visualised structures on the scan that were not present in the object investigated
- most can be avoided or reduced
What are the two main types of artefact?
- movement artefacts
- streak artefacts
What are movement artefacts, how do they appear and what can be done to reduce them?
- occur if patient is not completely still
- affects whole scan
- general blurriness
- extra contours
- reduced with fixation aids
- chin rest
- head strap
What are streak artefacts and what issues do they cause?
- caused by high attenuation objects
- primary metals
- amalgam
- primary metals
- main issues
- preventing caries assessment
- in adjacent restorations
- preventing endodontic assessment
- perforations
- missed canals
- preventing caries assessment
What contra-indications exist to CBCT?
- if plain radiographs are sufficient
- pathology requiring soft tissue visualisation
- malignancy
- infection spreading in soft tissue
- high risk of debilitating artefacts
- post retained crowns
- amalgam restorations
- metal ceramic crowns
- patient factors
- unable to stay still
- Parkinson’s disease
- certain learning difficulties
- uncooperative child
- patient unable to fit into machine
- kyphotic patient
- unfavourable neck to shoulder ratio
- obese
- bodybuilder
- unable to stay still
What training is required to carry out CBCT?
- UK undergraduate training is inadequate
- referring
- justifying
- interpreting
- postgraduate training is required
- level 1
- IRMER duty holders
- level 2
- justifying, performing or interpreting
- refresher training required
- every 5 years
- level 1
What is required for a CBCT to be justified?
- must be preceded by a clinical exam
- only used when plain radiograph is not sufficient
